#include <stdio.h>
int a[15]={15,14,13,12,11,10,9,8,7,6,5,4,3,2,1};
int main()
{
	int left=0,right=sizeof(a)/sizeof(int),x,coust=0,middle;
	printf("input number:");
	scanf("%d",&x);
	while(1)
	{
		middle=(left+right)/2;
		if(x==a[middle])
			break;
		if(x<a[middle])
		{
			left=middle+1;
		}else{
			right=middle-1;
		}if (left>right)
		{
			coust=1;
			break;
		}
	}
	if (coust==1)
	{
		printf("not number!\n");
	}else printf("%d\n",a[middle]);
	return 0;
}